Shift Significand of Decimal Floating Point Data

1. A computer program product for executing a machine instruction in a central processing unit, the computer program product comprising: a non-transitory computer readable storage medium readable by a processor and storing instructions for execution by the processor for performing a method comprising: obtaining a machine instruction for execution, the machine instruction being defined for computer execution according to a computer architecture, the machine instruction comprising an opcode, one register field, another register field, an index field, a base field and a displacement value; and performing a shift function on the significand of a decimal floating point datum as that function is defined by the opcode of the machine instruction, wherein the significand is stored in a location designated by the one register field, said shift function comprising: shifting in one direction one or more decimal digits of the significand a number of positions specified by a plurality of second operand bits determined using the index field, the base field and displacement value of the machine instruction, wherein the shifting comprises: expanding a portion of the significand in densely packed decimal into that portion of the significand in packed decimal; decoding a combination field of the decimal floating point datum into a biased exponent and another portion of the significand; combining the expanded portion of the significand and the another portion of the significand to create a working format significand; performing shifting on the working format significand; and in response to the performing, combining a portion of the working format significand and the biased exponent to obtain a new combination field, and converting another portion of the working format significand from packed decimal to densely packed decimal; and placing a result of the shift function in a location designated by the another register field.

2. The computer program product of claim 1 , wherein the one direction is to the left.

3. The computer program product of claim 1 , wherein the one direction is to the right.

4. The computer program product of claim 1 , wherein the portion of the significand being expanded is an encoded trailing significand of the decimal floating point datum.

5. The computer program product of claim 1 , wherein the another portion of the significand comprises a leftmost digit of the significand of the decimal floating point datum.

6. A method of executing a machine instruction in a central processing unit, said method comprising: obtaining, by a processor, a machine instruction for execution, the machine instruction being defined for computer execution according to a computer architecture, the machine instruction comprising an opcode, one register field, another register field, an index field, a base field and a displacement value; and performing a shift function on the significand of a decimal floating point datum as that function is defined by the opcode of the machine instruction, wherein the significand is stored in a location designated by the one register field, said shift function comprising: shifting in one direction one or more decimal digits of the significand a number of positions specified by a plurality of second operand bits determined using the index field, the base field and displacement value of the machine instruction, wherein the shifting comprises: expanding a portion of the significand in densely packed decimal into that portion of the significand in packed decimal; decoding a combination field of the decimal floating point datum into a biased exponent and another portion of the significand; combining the expanded portion of the significand and the another portion of the significand to create a working format significand; performing shifting on the working format significand; and in response to the performing, combining a portion of the working format significand and the biased exponent to obtain a new combination field, and converting another portion of the working format significand from packed decimal to densely packed decimal; and placing a result of the shift function in a location designated by the another register field.

7. The method of claim 6 , wherein the one direction is to the left.

8. The method of claim 6 , wherein the one direction is to the right.

9. The method of claim 6 , wherein the portion of the significand being expanded is an encoded trailing significand of the decimal floating point datum.

10. The method of claim 6 , wherein the another portion of the significand comprises a leftmost digit of the significand of the decimal floating point datum.

11. A system of executing a machine instruction in a central processing unit, said system comprising: a memory; and a processor in communications with the memory, wherein the computer system is configured to perform a method, said method comprising: obtaining a machine instruction for execution, the machine instruction being defined for computer execution according to a computer architecture, the machine instruction comprising an opcode, one register field, another register field, an index field, a base field and a displacement value; and performing a shift function on the significand of a decimal floating point datum as that function is defined by the opcode of the machine instruction, wherein the significand is stored in a location designated by the one register field, said shift function comprising: shifting in one direction one or more decimal digits of the significand a number of positions specified by a plurality of second operand bits determined using the index field, the base field and displacement value of the machine instruction, wherein the shifting comprises: expanding a portion of the significand in densely packed decimal into that portion of the significand in packed decimal; decoding a combination field of the decimal floating point datum into a biased exponent and another portion of the significand; combining the expanded portion of the significand and the another portion of the significand to create a working format significand; performing shifting on the working format significand; and in response to the performing, combining a portion of the working format significand and the biased exponent to obtain a new combination field, and converting another portion of the working format significand from packed decimal to densely packed decimal; and placing a result of the shift function in a location designated by the another register field.

12. The computer system of claim 11 , wherein the one direction is to the left.

13. The computer system of claim 11 , wherein the one direction is to the right.

14. The computer system of claim 11 , wherein the portion of the significand being expanded is an encoded trailing significand of the decimal floating point datum.

15. The computer system of claim 11 , wherein the another portion of the significand comprises a leftmost digit of the significand of the decimal floating point datum.